Variation and natural selection

• How is variation caused?

  By alleles being inherited during sexual reproduction
• Define species 


  Organisms that are similar enough to breed and produce fertile offspring
• Describe natural selection


  • Organisms in a species show variation in their characteristics as a result of mutations
  • There is competition for a resource within a population
  • Individuals with the most suitable characteristics for the environment are more successful so are more likely to survive and reproduce
  • Successful organisms that survive and reproduce pass on the genes for the favourite characteristics to their offspring
  • Overtime, the beneficial characteristics become more common and the species change
• What is variation?


  The differences in the characteristics of all individuals in a population.
• Name 2 other causes of variation:

  Environment (e.g colour of flowers depends on the pH of soil)

  A combination of genes and the environment
• What is genetic variation caused by?

  Mutations
• What is meant by genotype?

  Letters used to determine characteristics e.g Bb BB bb
• What is meant by phenotype?

  Physical descriptions using words that describe genotypes e.g Blue eyes